There is a critical need for the development of cheap and effective drugs against trypanosomiasis and leishmaniasis. Specific inhibitors of parasite tubulin, a known drug target for anticancer and anthelmintic agents, would be of great interest as chemotherapeutic candidates against these diseases. We have thus set out to test the hypothesis that tubulin can be exploited as a target for selective antitrypanosomal and antileishmanial chemotherapy. In support of this hypothesis, our laboratory has identified Nl-aryl-N4- dialkyl-3, 5-dinitro sulfanilamides as potent and selective ligands for tubulin from Leishmania and trypanosomes. Our best compounds in this series are effective in vitro against T. brucei at mid-nanomolar concentrations and against L. donovani at low micromolar levels, interfere with parasite cell division at IC50 concentrations, selectively block the in vitro assembly of purified leishmanial tubulin at low micromolar levels, and possess an in vitro selectivity of two orders of magnitude for African trypanosomes over mammalian cell lines. In attempts toward achieving our long-term goal on this project, to develop new antiparasitic drugs that selectively target kinetoplastid tubulin, we propose the following Specific Aims: 1. Synthetic optimization of our simple antimitotic antiparasitic agents by creating a focused library of over 500 Nl-aryl-N4-dialkyl-3,5-dinitro sulfanilamides prepared by parallel synthesis. Replacement of the nitro groups will also be investigated through traditional synthetic methods. 2. Evaluation of the target compounds for antiparasitic efficacy, selectivity, and antimitotic activity. Established in vitro protocols will allow us to efficiently select the most promising antimitotic agents against African trypanosomes, American trypanosomes, and Leishmania, while animal studies will examine the in vivo antitrypanosomal efficacy and pharmacokinetics of promising compounds. 3. Identification of the binding site of our antimitotic agents through computer modeling and the structure based design of new classes of selective antitubulin agents. These studies will provide insight into the molecular basis for the specificity of our current compounds and will also present an opportunity to identify novel agents with selective antimitotic antiparasitic activity that could serve as drug candidates.